The present invention relates to an image display apparatus that displays input image data.
In a display device that uses backlight without emitting light by itself as in liquid crystals, power consumption of the backlight occupies most of that of the display device in many cases. In this case, reduction in the power consumption of the backlight has the key to that of the entire display device.
For the purpose, a processing where the light quantity of the backlight is reduced in a dark video scene is performed, and thereby, attempts are made to reduce the power consumption of the display device. When the light quantity of the backlight is simply reduced to 1/N, the brightness of the screen is also decreased to 1/N if nothing is done. However, the light quantity of the backlight is reduced to 1/N, and further, a pixel value of each pixel is corrected to thereby increase transmissivity of each liquid crystal pixel to N times. By doing so, the brightness of the screen can be finally maintained.
However, the transmissivity of each liquid crystal pixel cannot be set to a value greater than a maximum transmissivity that is feasible in liquid crystal elements. Therefore, an upper limit exists in a value of N. For the purpose of maximizing N in a range where the degradation in the image quality is prevented from occurring, the value of N may be adjusted such that the transmissivity of a liquid crystal pixel corresponding to a brightest pixel in a display image is set to the maximum transmissivity of the liquid crystal element. As described above, a method of collectively controlling backlight luminance of the entire screen as described above is referred to as global dimming.
In the global dimming, even if one luminescent spot is present in the screen, the value of N is affected by the luminescent spot and the luminance of the entire backlight increases. Therefore, an effect of the reduction in the power consumption is hard to be exerted too much depending on contents of the video in some cases.
To cope with the above-described problem, recently, watched is a technology called local dimming in which a screen is divided into small areas, a light source corresponding to each small area is prepared on one-on-one level, the light emission intensity of each light source can be independently controlled, and thereby, the luminance of the backlight is controlled to each area (“Locally Pixel-compensated backlight dimming on LED-backlight LCD TV”, Hanfeng Chen et al., Journal of the SID 2007 pp 981-988). Based on a pixel value in the area using the same manner as in the global dimming technology, the light emission intensity of a light source corresponding to each area is determined in this technology. This operation is performed over all the areas within the screen, thereby determining the light emission intensities of all the light sources. Using these values, each light source is controlled, and at the same time, each pixel value of input images is compensated in the same manner as in the global dimming technology. Thereby, the power consumption can be reduced without almost deteriorating quality of the video.
It is desired that when the global dimming technology is performed, light emitted from each light source is uniformly irradiated on the corresponding area, and further, light emitted from the other light sources has no effect on a luminance distribution within the area. However, light emitted from each light source actually extends also over other areas in many cases. In this case, when light emitted from the light source corresponding to the area is irradiated on the area and light emitted from light sources near the area is not irradiated on the area, the original luminance of the backlight in the area cannot be attained in some cases. Also under the above-described conditions, as a method of assuring the necessary backlight luminance, in JP-A-2008-9415, provided is a method of emitting light from ambient light sources with a value obtained by multiplying the light emission intensity by a certain constant value at the time of emitting light from a certain light source.